Could you please share a picture of your battery connection. Are you using a capacitor? Have you had any issues with the BMW battery monitoring because of the amplifiers drawing current from the battery?

I just recently got my X1 and have been making plans on improving the Hifi-system (which is the non HK Hifi option).

Thanks, I'm glad to help you...
Tomorrow i try to post the picture of the battery, I used a couples of awg 8 cables, for my amplifiers are enought. I'm using Pioneer d class amplifier.
Actually i don't use a capacitor, my amplifiers require very low current.
Never had issues with Bmw system, I just recharge sometime the battery with a C tek mxs 5.0 just to increase its life.
My last upgrade is the installation of a 13cm midwoofer (Focal 5k1) in the door. Maybe next idea is create a reflex box on the lower part of the door to install a Scan Speak 15w revelator.
Depend how much you want to improve...if you install a gladen bmw system with 4 channel amplifier you can obtain a nice sound, if you want more (detail, stabel and precise sound stage etc...) i suggest to install a processor and create a multiamplified system with oriented speakers.